1. Field of the Invention
The present invention relates generally to self-healing cables for a variety of applications (e.g., electrical, optical, fluid, gas, etc.), and particularly to self-healing cables for extreme environments.
2. Technical Background
Self-healing cable failures are a major concern in high-performance engineered systems such as cars, airplanes, boats, submarines, spacecraft, nuclear power plants, buildings, etc. For example, cabling problems on commercial and military aircraft have been implicated as the cause of accidents. Self-healing cable failures can occur for a number of reasons, such as the result of physical chafing, vibration, and wires in bundles rubbing against each other. These actions are examples of damaging forces that can cause a self-healing cable to become cracked and broken, and in the case of electrical wiring may cause shorts, sparks, incorrect signals, fire, and arcing, among many other possible electrical failures.
Even though self-healing cable failure poses a significant safety hazard in many different applications, self-healing cable inspection and repair remains difficult and expensive. Hidden self-healing cable damage is difficult to locate, and the self-healing cable inspection process itself can itself cause self-healing cable damage. Self-healing cable replacement is often quicker than diagnosis and repair.
Of particular concern is self-healing cable failure in extreme environments, i.e., environments that experience extremes in one or more environmental characteristics, such temperature, pressure, and acceleration (particularly vibration). Such extreme environments occur, for example, in aviation and aeronautical applications. Not only does an extreme environment exacerbate self-healing cable failure issues, it also prevents most types of self-healing cables developed for use the utility and construction industries from operating properly. For example, U.S. Patent Publication No. US2005/0136257 to Easter discloses a self-healing cable that has a water-swellable composition surrounding a conductor. When the self-healing cable is damaged, the water-swellable material reacts with water and seals the breach in the self-healing cable. However, this approach will not work in an extreme environment wherein the temperature can swing below the freezing point of water. Nor will it work in an environment where liquid water is absent.
Another issue related to cabling used in extreme environments is that such cabling needs to satisfy higher design standards and specifications. For example, aviation and aerospace cabling needs to satisfy U.S. Military Specification No. 22759, which has a variety of requirements, such for temperature (down to −55° C.), extreme bending, dielectric strength, etc. Thus, any self-healing cable used in an extreme environment needs to perform at or near such stringent requirements. The prior art self-healing cables are typically suitable for select environments that do not experience a wide variation in environmental conditions experienced in extreme environments and so are unsuitable for extreme environment applications.